Conventionally, the tire pressure monitoring system (TPMS) detects the tire pressure and warns the driver by a warning display on a meter panel when the detected tire pressure is lower than a threshold. Besides, as disclosed in Japanese patent document JP-A-2005-254932, or other Japanese patent documents such as JP-A-2008-163633 (i.e., now available as US 20080157919) and JP-A-2008-213514 (i.e., now available as US 200800204281), some monitoring systems display the detected tire pressure as a short-term pressure transition graph on a display of a navigation system, based on the tire pressure detected by pressure detectors disposed on each of the tires.
Further, tire pressure is, in association with an economical travel of the vehicle, now more frequently checked for the increase of the fuel mileage. That is, in other words, tire pressure adjustments performed by the driver in an easy manner are now highly recommended and desired.
However, the TPMS is generally designed to warn the driver of the decrease of the tire pressure during the travel of the vehicle, thereby making it impossible to detect the tire pressure while the ignition switch of the vehicle is turned off. Moreover, the detected tire pressure can, only be displayed on a meter panel of the vehicle. Therefore, in order to check the tire pressure by using the conventional TPMS, the driver must first turn on the ignition switch of the vehicle and then peek into the meter panel.
Further, the conventional TPMS in the above Japanese patent document (i.e., the first one) displays the graph (i.e., the tire pressure information) on the display of the navigation system. Therefore, the tire pressure information cannot be viewed when the ignition switch of the vehicle is not turned on (i.e., when the navigation system is not having a power supply). In other words, the power supply for the navigation system has to be turned on by the ignition switch, only for the display of the tire pressure information. The user may otherwise use a tire gauge for checking the tire pressure. In this case, the user must purchase the tire gauge by him/herself.
That is, in other words, the conventional TPMS does not allow the user to easily and promptly check the tire pressure.